Substrate inspection apparatus, substrate inspection method and method of manufacturing semiconductor device

ABSTRACT

A substrate inspection apparatus includes: an electron beam irradiation device which emits an electron beam and causes the electron beam to irradiate a substrate to be inspected as a primary beam; an electron beam detector which detects at least one of a secondary electron, a reflected electron and a backscattered electron that are generated from the substrate that has been irradiated by the electron beam, and which outputs a signal that forms a one-dimensional or two-dimensional image of a surface of the substrate; a mapping projection optical system which causes imaging of at least one of the secondary electron, the reflected electron and the backscattered electron on the electron beam detector as a secondary beam; and an electromagnetic wave irradiation device which generates an electromagnetic wave and causes the electromagnetic wave to irradiate a location on the surface of the substrate at which the secondary beam is generated.

CROSS REFERENCE TO RELATED APPLICATION

This is a division of Application Ser. No. 10/853,678, filed May 26,2004 now U.S. Pat. No. 7,211,796, which is incorporated herein byreference.

This application claims benefit of priority under 35USC § 119 toJapanese Patent Applications No. 2003-149172, filed on May 27, 2003, andNo. 2003-149416, filed on May 27, 2003, the contents of which areincorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a substrate inspection apparatus, asubstrate inspection method, and a method of manufacturing asemiconductor device, with the objective of observing or inspecting, forexample, a semiconductor pattern by use of an electron beam.

2. Related Background Art

Methods of inspecting defects in semiconductor patterns with the use ofelectron beams have recently been developed and are now in use. One suchmethod, disclosed in Japanese Patent Laid Open No. 7-249393 by way ofexample, involves generating a rectangular electron beam as a primarybeam by electron irradiation means and irradiating the specimentherewith, then projecting an enlarged image of secondary electrons andbackscattered electrons generated from the specimen surface, as asecondary beam, by mapping projection optical means and obtaining animage of the specimen surface indicative of changes in theshape/properties/potential of the specimen surface by an electrondetection means such as an MCP detector. In addition to that method,another method has been proposed in Japanese Patent Laid-Open No.11-132975, for example, by which the primary beam is deflected by a Wienfilter so as to be incident on the specimen surface, and also asecondary beam is allowed to proceed through the same Wien filter andenters mapping optical projection means.

However, the inspection process disclosed in Japanese Patent Laid-OpenNo. 11-132975 for example has a problem in that, when the primary beamis shone onto the specimen, local differences in the charge state of thespecimen surface will be created, depending on the shape and propertiesof the specimen surface or the layers in the vicinity thereof, and thusthe inspection characteristics will deteriorate due to the resultantlocal differences in potential. This point will now be discussed withreference to the accompanying figures. Note that the same portions inthe figures discussed below are denoted by the same reference numbersand description thereof is repeated only when necessary.

As shown in FIG. 27, if there are portions 202 and 204 of mutuallydifferent potentials in a surface layer of a specimen S, potentialgradients that are not parallel to the surface of the specimen S aregenerated in regions R_(D1) and R_(D2) above the vicinity of boundarysurfaces C1 and C2 between the portions 202 and 204. When the secondarybeams that are emitted in the vicinity of the boundaries C1 and C2 arecontrolled by a secondary optical system of the inspection apparatus toform an image on a detection surface of the detector, these potentialgradients will exert an unwanted deflection effect on the secondarybeams, hindering appropriate imaging and causing distortion and contrastdeterioration in the detected image. This phenomenon is particularlyobvious in the inspection of interconnection patterns for large-scaleintegrated circuits (LSIs). This is because, in LSI interconnections,each portion 202 of FIG. 27 corresponds to e.g. an insulator of SiO₂ orthe like and the portion 204 corresponds to e.g. a conductor of tungsten(W) or the like, so the charging of each insulator during irradiation byan electron beam will create a large potential difference with respectto the conductor.

Occurrence of such local potential differences is not limited toboundary surfaces between different materials in mutual contact. Forexample, even if there are insulating portions 214 between the metalwiring 212 on the specimen S of an integrated circuit wafer, as shown inFIG. 28, if the primary beam irradiates with an incident energy (energyof electrons that are directly incident on the specimen S) that gives atotal secondary electron emission ratio σ for each insulating portion214 of 1 or more, the surface of the insulating portion 214 will bepositively charged. Such incident energy is about 50 eV to 1 keV if thematerial of the insulating portion 214 is SiO₂, by way of example. Insuch a case, local potential gradients that are not parallel to thesurface of the specimen S are generated in the vicinity of a boundary216 between the metal wiring 212 and the insulating portion 214. Thesepotential gradients will exert an inappropriate deflection effect onsecondary electrons emitted with a low emission energy of no more than afew eV from each of a point P2 within the metal wiring 212 in thevicinity of the boundary 216 and a point P4 within the insulatingportion 214 in the vicinity of the boundary 216, before they are imagedon the MCP detector by the secondary optical system. This will make thetrajectories of the secondary electrons deviate from electron beamtrajectories TJ_(IP2) and TJ_(IP4) that are ideal for accurate mappingprojection and curve as shown by trajectories TJ_(RP6) and TJ_(RP8). Asa result, accurate imaging of the secondary beam is hindered, raising aproblem in that the accuracy of defect detection is adversely affectedby distortion and contrast deterioration of the detected image.

In general, the following three characteristics are mainly required of adetected image of a secondary beam, in order to improve the defectinspection capabilities when using electron beams:

-   1) Distortion must be small;-   2) The S/N ratio (the ratio of electrons that contribute to the    imaging to noise electrons that do not contribute to the imaging,    within the secondary beam signal that arrives at the detector from    the material that is the specimen surface) must be large; and-   3) The contrast between different materials must be large.

BRIEF SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provideda substrate inspection apparatus comprising:

an electron beam irradiation device which emits an electron beam andcauses the electron beam to irradiate a substrate to be inspected as aprimary beam;

an electron beam detector which detects at least one of a secondaryelectron, a reflected electron and a backscattered electron that aregenerated from the substrate that has been irradiated by the electronbeam, and which outputs a signal that forms a one-dimensional ortwo-dimensional image of a surface of the substrate;

a mapping projection optical system which causes imaging of at least oneof the secondary electron, the reflected electron and the backscatteredelectron on said electron beam detector as a secondary beam; and

an electromagnetic wave irradiation device which generates anelectromagnetic wave and causes the electromagnetic wave to irradiate alocation on the surface of the substrate at which the secondary beam isgenerated.

According to a second aspect of the present invention, there is provideda substrate inspection apparatus comprising:

an electron beam irradiation device which emits an electron beam andcauses the electron beam to irradiate a substrate to be inspected thathas an insulator formed thereon as a primary beam under a condition suchthat the insulator is negatively charged;

an electron beam detector which detects at least one of a secondaryelectron, a reflected electron and a backscattered electron that aregenerated from the substrate that has been irradiated by the primarybeam and which outputs a signal that forms a one-dimensional ortwo-dimensional image of a surface of the substrate; and

a mapping projection optical system which causes imaging of at least oneof the secondary electron, the reflected electron and the backscatteredelectron on said electron beam detector.

According to a third aspect of the present invention, there is provideda substrate inspection method comprising:

emitting an electron beam and causing the electron beam to irradiate asubstrate to be inspected as a primary beam;

projecting at least one of a secondary electron, a reflected electronand a backscattered electron that are generated from the substrate thathas been irradiated by the electron beam, as a secondary beam to causeimaging of the secondary beam;

detecting an image caused by said imaging of the secondary beam andoutputting a signal to form a one-dimensional or two-dimensional imageof a surface of the substrate; and

generating an electromagnetic wave and causes the electromagnetic waveto irradiate a location on the surface of the substrate at which thesecondary beam is generated.

According to a fourth aspect of the present invention, there is provideda substrate inspection method comprising:

emitting an electron beam and causing the electron beam to irradiate asubstrate to be inspected that has an insulator formed thereon as aprimary beam under a condition such that the insulator is negativelycharged;

projecting at least one of a secondary electron, a reflected electronand a backscattered electron that are generated from the substrate thathas been irradiated by the primary beam, as a secondary beam to causeimaging of the secondary beam; and

detecting an image caused by said imaging of the secondary beam andoutputting a signal to form a one-dimensional or two-dimensional imageof a surface of the substrate.

According to a fifth aspect of the present invention, there is provideda method of manufacturing a semiconductor device comprising a substrateinspection method, said substrate inspection method including:

emitting an electron beam and causing the electron beam to irradiate asubstrate to be inspected as a primary beam;

projecting at least one of a secondary electron, a reflected electronand a backscattered electron that are generated from the substrate thathas been irradiated by the electron beam, as a secondary beam to causeimaging of the secondary beam;

detecting an image caused by said imaging of the secondary beam andoutputting a signal to form a one-dimensional or two-dimensional imageof a surface of the substrate; and

generating an electromagnetic wave and causes the electromagnetic waveto irradiate a location on the surface of the substrate at which thesecondary beam is generated.

According to a sixth aspect of the present invention, there is provideda method of manufacturing a semiconductor device comprising a substrateinspection method, said substrate inspection method including:

emitting an electron beam and causing the electron beam to irradiate asubstrate to be inspected that has an insulator formed thereon as aprimary beam under a condition such that the insulator is negativelycharged;

projecting at least one of a secondary electron, a reflected electronand a backscattered electron that are generated from the substrate thathas been irradiated by the primary beam, as a secondary beam to causeimaging of the secondary beam; and

detecting an image caused by said imaging of the secondary beam andoutputting a signal to form a one-dimensional or two-dimensional imageof a surface of the substrate.

According to a seventh aspect of the present invention, there isprovided a substrate inspection apparatus comprising:

an electron beam irradiation device which emits an electron beam andcauses the electron beam to irradiate a substrate to be inspected as aprimary beam;

an electron beam detector which exclusively detects a reflected electronamong electrons generated from the substrate that has been irradiated bythe primary beam, said reflected electron having an energy immediatelyafter generation thereof substantially equivalent to an incident energyof the primary beam; and

a mapping projection optical system which projects said reflectedelectron exclusively as a secondary beam and causes imaging of thesecondary beam on said electron beam detector to an inspection image ofone or two dimension.

According to an eighth aspect of the present invention, there isprovided a substrate inspection apparatus comprising:

an electron beam irradiation device which emits an electron beam andcauses the electron beam to irradiate a substrate to be inspected as aprimary beam;

an electron beam detector which detects a reflected electron amongelectrons generated from the substrate that has been irradiated by theprimary beam, said reflected electron having an energy immediately aftergeneration thereof substantially equivalent to an incident energy of theprimary beam;

a mapping projection optical system which projects said reflectedelectron as a secondary beam and causes imaging of the secondary beam onsaid electron beam detector as an inspection image of one or twodimension; and

a controller which controls at least one of said electron beamirradiation device, said mapping projection optical system and saidelectron beam detector on the basis of at least one of a first, a secondand a third estimated values, said first estimated value beingrepresentative of an extent of distortion of the inspection image, saidsecond estimated value being representative of a S/N of a signaloutputted from said electron beam detector, and said third estimatedvalue being representative of an extent of difference in contrast amongmaterials in the inspection image when an area of the substrate to beinspected is constituted of a plurality of different materials.

According to a ninth aspect of the present invention, there is provideda substrate inspection method comprising:

emitting an electron beam and causing the electron beam to irradiate asubstrate to be inspected as a primary beam;

projecting exclusively a reflected electron among electrons generatedfrom the substrate that has been irradiated by the primary beam, as asecondary beam to cause imaging of the secondary beam to an inspectionimage of one or two dimension, said reflected electron having an energyimmediately after generation thereof substantially equivalent to anincident energy of the primary beam; and

detecting said reflected electron at said imaging of the secondary beamto output a signal to form the inspection image of one or two dimension.

According to a tenth aspect of the present invention, there is provideda substrate inspection method comprising:

emitting an electron beam and causing the electron beam to irradiate asubstrate to be inspected as a primary beam;

projecting a reflected electron among electrons generated from thesubstrate that has been irradiated by the primary beam, as a secondarybeam to cause imaging of the secondary beam to an inspection image ofone or two dimension, said reflected electron having an energyimmediately after generation thereof substantially equivalent to anincident energy of the primary beam;

detecting said reflected electron at said imaging of the secondary beamto output a signal to form the inspection image of one or two dimension;and

controlling at least one of the irradiation of the primary beam, atrajectory of the secondary beam and the detection of the electrons onthe basis of at least one of a first, a second and a third estimatedvalues, said first estimated value being representative of an extent ofdistortion of the inspection image, said second estimated value beingrepresentative of a S/N of the signal to form the inspection image, andsaid third estimated value being representative of an extent ofdifference in contrast among materials in the inspection image when anarea of the substrate to be inspected is constituted of a plurality ofdifferent materials.

According to an eleventh aspect of the present invention, there isprovided a method of manufacturing a semiconductor device comprising asubstrate inspection method, said substrate inspection method including:

emitting an electron beam and causing the electron beam to irradiate asubstrate to be inspected as a primary beam;

projecting exclusively a reflected electron among electrons generatedfrom the substrate that has been irradiated by the primary beam, as asecondary beam to cause imaging of the secondary beam to an inspectionimage of one or two dimension, said reflected electron having an energyimmediately after generation thereof substantially equivalent to anincident energy of the primary beam; and

detecting said reflected electron at said imaging of the secondary beamto output a signal to form the inspection image of one or two dimension.

According to a twelfth aspect of the present invention, there isprovided a method of manufacturing a semiconductor device comprising asubstrate inspection method, said substrate inspection method including:

emitting an electron beam and causing the electron beam to irradiate asubstrate to be inspected as a primary beam;

projecting a reflected electron among electrons generated from thesubstrate that has been irradiated by the primary beam, as a secondarybeam to cause imaging of the secondary beam to an inspection image ofone or two dimension, said reflected electron having an energyimmediately after generation thereof substantially equivalent to anincident energy of the primary beam;

detecting said reflected electron at said imaging of the secondary beamto output a signal to form the inspection image of one or two dimension;and

controlling at least one of the irradiation of the primary beam, atrajectory of the secondary beam and the detection of the electrons onthe basis of at least one of a first, a second and a third estimatedvalues, said first estimated value being representative of an extent ofdistortion of the inspection image, said second estimated value beingrepresentative of a S/N of the signal to form the inspection image, andsaid third estimated value being representative of an extent ofdifference in contrast among materials in the inspection image when anarea of the substrate to be inspected is constituted of a plurality ofdifferent materials.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a substrate inspection apparatus inaccordance with a first embodiment of the present invention;

FIG. 2 is a perspective view of a specific configuration of the Wienfilter comprised by the substrate inspection apparatus of FIG. 1;

FIGS. 3 and 4 are illustrative of the operating principle of the Wienfilter of FIG. 2;

FIG. 5 is a schematic view illustrating a substrate inspection method inaccordance with a second embodiment of the present invention;

FIG. 6 is illustrative of energy bands of the insulator of FIG. 5;

FIG. 7 is a schematic view illustrating a substrate inspection method inaccordance with a third embodiment of the present invention;

FIG. 8 is illustrative of energy bands in the junction between the metaland the insulator of FIG. 7;

FIG. 9 is a block diagram of a substrate inspection apparatus inaccordance with the third embodiment of the present invention;

FIG. 10 is a graph of an example of the relationship between incidentenergy of an electron beam on SiO₂ and the total secondary electronemission ratio;

FIG. 11 is illustrative of the effects obtained by the substrateinspection method of a fourth embodiment of the present invention;

FIG. 12 is illustrative of a problem that occurs if the primary beamirradiates the insulator on the specimen surface too much, undernegative charging conditions;

FIG. 13 is a table of combinations of electron beam irradiationconditions in the substrate inspection apparatus of FIG. 9;

FIG. 14 is a block diagram of a variant example of the substrateinspection apparatus of FIG. 9;

FIG. 15 shows the energy distributions of emitted electrons

FIG. 16 shows the relationship between the incident energy of theprimary beam and the distortion and S/N ratio of the electron image;

FIG. 17 is a block diagram of the basic configuration of a substrateinspection apparatus in accordance with a fifth embodiment of thepresent invention;

FIG. 18 is a block diagram of a specific configuration of the hostcomputer comprised by the substrate inspection apparatus of FIG. 17;

FIG. 19 is a flowchart of the basic sequence of the substrate inspectionmethod in accordance with the fifth embodiment of the present invention;

FIG. 20 is a block diagram of the basic configuration of a substrateinspection apparatus in accordance with a sixth embodiment of thepresent invention;

FIG. 21 is a block diagram of the basic configuration of a substrateinspection apparatus in accordance with a seventh embodiment of thepresent invention;

FIG. 22 is a perspective view of the noise electron shield electrode ofthe substrate inspection apparatus of FIG. 21;

FIG. 23A is a plan view of the noise electron shield electrode of FIG.21 and FIG. 23B is a section through the noise electron shield electrodeof FIG. 21;

FIG. 24 is a perspective view of an example of a noise electron shieldelectrode of a grid (mesh) shape;

FIG. 25A is a plan view of the noise electron shield electrode of FIG.24 and FIG. 25B is a section through the noise electron shield electrodeof FIG. 24;

FIG. 26 is a block diagram of the basic configuration of a substrateinspection apparatus in accordance with an eighth embodiment of thepresent invention;

FIG. 27 illustrates a problem with a substrate inspection method inaccordance with a conventional technique; and

FIG. 28 illustrates another problem with the substrate inspection methodin accordance with a conventional technique.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention are described below with referenceto the accompanying drawings.

First Embodiment

A block diagram of the basic configuration of a substrate inspectionapparatus in accordance with a first embodiment of the present inventionis shown in FIG. 1. A substrate inspection apparatus 1 shown in thisfigure comprises a primary optical system 10, a Wien filter 41, asecondary optical system 20, an electron detector 30, an image signalprocessor 58, a host computer 60, a display section 59, a stage 43, astage driver 47, and various controllers 16, 17, and 51 to 57, togetherwith a laser beam irradiation device 122 that is specific to thisembodiment.

The primary optical system 10 includes an electron gun section 11 and aplurality of stages of quadrupole lenses 15. The electron gun section 11has an LaB₆ linear cathode 112 having a rectangular electron emissionsurface of 100 μm to 700 μm along the long axis and 15 μm along theshort axis, a Wehnelt electrode 114, an anode 116 for electron beamextraction, and a deflector 118 for adjusting the optical axis. Theacceleration voltage, radiation current and the optical axis of aprimary beam Bp are controlled by an electron gun controller 16. Theelectron gun controller 16 is connected to the host computer 60 andreceives control signals supplied there from. A plurality of stages ofquadrupole lenses 15 is controlled by a multi-stage quadrupole lenscontroller 17 to focus the primary beam Bp emitted from the linearcathode 112 and control the trajectory thereof so that it is incidentfrom an angle on the Wien filter 41. The multi-stage quadrupole lenscontroller 17 is also connected to the host computer 60 and receivescontrol signals supplied there from.

The Wien filter 41 receives control signals from the host computer 60through a Wien filter controller 53, and deflects the primary beam Bpentering from the primary optical system 10 to make it incidentsubstantially perpendicular to the surface of a the specimen S. Theprimary beam Bp that has passed through the Wien filter 41 is subjectedto the lens action of a cathode lens 21 that is a rotationallysymmetrical electrostatic lens so that it irradiates the surface of thespecimen S perpendicularly.

The specimen S is disposed on the stage 43, with the configuration beingsuch that a negative voltage can be applied thereto by a stage voltagecontroller 51 through this stage 43. The objective of this mechanism isto reduce incident damage to the specimen S by the primary beam Bp andincrease the energy of a secondary beam Bs formed of secondaryelectrons, reflected electrons, and backscattered electrons that aregenerated by variations in the shape, properties, or potential of thesurface of the specimen by the irradiation of the primary beam Bp. Thestage 43 receives control signals supplied from the stage driver 47 andmoves in a direction D_(SS) (indicated by an arrow in FIG. 1 for thisembodiment) so that the surface of the specimen S is scanned with theprimary beam Bp.

A specific configuration of the Wien filter 41 is shown in FIG. 2 andthe operating principle thereof is illustrated in FIGS. 3 and 4. Asshown in FIG. 2, the electromagnetic field of the Wien filter 41 has aconfiguration in which an electrical field E and a magnetic field B areperpendicular to each other within a plane that is orthogonal to theoptical axis (Z axis) of a secondary optical system, so that only thoseelectrons of an incident electron beam Bp that satisfy the Wiencondition qE=vB (where q is the charge of an electron and v is thevelocity of a moving electron) are allowed to proceed. As shown in FIG.3, in the substrate inspection apparatus 1, a force F_(B) by themagnetic field and a force F_(E) by the electrical field act on theprimary beam Bp in the same direction, causing the primary beam Bp todeflect so that it is incident perpendicularly to the specimen S. On theother hand, regarding the secondary beam Bs, the forces F_(B) and F_(E)act on in opposite directions, and also the Wien condition F_(B)=F_(E)is satisfied, therefore, the secondary beam Bs is not deflected and soproceeds onward and enters the secondary optical system 20.

Returning to FIG. 1, the secondary optical system 20 includes thecathode lens 21 which is a rotationally symmetrical electrostatic lens,a second lens 22, a third lens 23, a fourth lens 24, a numericalaperture 25 which is disposed within a horizontal plane 9 that isperpendicular to the optical axis As of the secondary optical systembetween the Wien filter 41 and the cathode lens 21, and a field aperture26 which is installed between the second lens 22 and the third lens 23.The cathode lens 21, the second lens 22, the third lens 23, and thefourth lens 24 are controlled by a cathode lens controller 52, a secondlens controller 54, a third lens controller 55, and a fourth lenscontroller 56, respectively, to perform projection imaging of thesecondary beam Bs. The cathode lens 52, the second lens controller 54,the third lens controller 55, and the fourth lens controller 56 eachreceive various control signals that are supplied from the host computer60 connected thereto. With the apparatus configuration shown in FIG. 1,the numerical aperture 25 is disposed at a position in the horizontalplane 9 that suppresses amplified color aberrations of the secondarybeam Bs, and this ensures that the cathode lens 21 and the second lens22 combine to perform a single image of the secondary beam Bs. Sincethis configuration also means that the irradiation region of the primarybeam Bp on the specimen S is limited by the numerical aperture 25, aKoeller illumination system is used to control the trajectory of theprimary beam Bp in the space between the numerical aperture 25 and thespecimen S in such a manner that the primary beam Bp focuses on thenumerical aperture iris 25 which, in addition to the following lensaction of the cathode lens 21, makes it irradiate the specimen Ssubstantially perpendicularly.

The electron detector 30 includes a micro-channel plate (MCP) detector31, a fluorescent plate 32, a light guide 33, and a capture element 34such as a charge-coupled device (CCD). The secondary beam Bs that isincident on the MCP detector 31 is amplified by the MCP and irradiatesthe fluorescent plate 32. The capture element 34 detects a fluorescentimage generated by the fluorescent plate 32, through the light guide 33,and sends a detection signal to the image signal processor 58. The imagesignal processor 58 processes the detection signal and supplies it tothe host computer 60 as image data representing an image of one or twodimension. The host computer 60 processes the thus-supplied image data,displays the image on the display section 59. It also saves the imagedata and uses various image processing techniques to detect whether ornot there are defects in the specimen S and, if defects are detected,outputs an evaluation of their severity.

A laser beam irradiation device 120 is installed in the vicinity of thesecondary optical system 20, to reduce the local potential difference ofthe surface of the specimen S by generating a laser beam for shining onthe specimen S. The laser beam irradiation device 120 corresponds to,for example, an electromagnetic radiation device, and includes a laserbeam source 122 that generates a laser beam L, and a power source 124that supplies electrical power to the laser beam source 122. The axis ALof the laser beam is set to join at an intersection IP₀ of the surfaceof the specimen S and of the optical axis As of the secondary opticalsystem, and this ensures that the laser beam L emitted by the laser beamsource 122 irradiates the center of the inspection region of the surfaceof the specimen that is irradiated by the primary beam Bp. Adjustment ofthe laser beam axis AL is done by disposing a sensor for detecting alaser parameter or the like of the laser beam at the position of theintersection IP₀, and monitoring the output there from while adjustingthe laser beam source to obtain the largest value of the output.

When the primary beam Bp is shone onto the surface of the specimen Sduring the inspection, local differences will occur in the magnitude ofcharge on the surface of the specimen S, depending on the shape andproperties of the surface of the specimen S or the layers in thevicinity of that surface. In particular, if there is an insulator in thesurface of the specimen S, the charge magnitude will increase and therewill also be many places in which those charges (electrons and holes)cannot migrate (be neutralized).

In such a case, according to this embodiment the laser beam L from thelaser beam source 122 enables resident charges or peripheral charges toabsorb the energy of the laser beam L, putting them into a state thatfacilitates migration, and, as a result, makes it possible to reducelocal charges at charged locations on the specimen surface (even if thecharge magnitude of the insulator as a whole does not change) reducinglocal potential differences.

Specific methods of reducing such local potential differences include:

-   1) A method of irradiating the entire insulator charge location with    electromagnetic waves having energy that enables conduction;-   2) A method of irradiating with electromagnetic waves imparted with    energy that enables the migration of electrons and holes that have    been immobilized at the local level of the insulator; and-   3) A method of reducing charge in the vicinity of boundaries between    different materials on the specimen surface.

These methods are described below within the second and thirdembodiments of the present invention.

Second Embodiment

The description turns to a substrate inspection method in accordancewith a second embodiment of the present invention, with reference toFIG. 5. The surface of an insulator IS1 shown on the left-hand side ofthe figure is charged locally by a positive charge. On the surface ofthe insulator IS1 on the right-hand side of the figure, there areelectrons and holes that have been immobilized at the local level. Notethat this local charging and the immobilization of electrons and holesat the local level are not limited to insulating regions; it can alsooccur in semiconductor regions.

An energy band diagram of the insulator IS1 is shown in FIG. 6. Toenable the migration of local charges in the insulator IS1, a laser beam(electromagnetic waves) L1 having energy of at least the same magnitudeas the band gap Eg of the insulator could be shone thereon, to cause thegeneration of electron-hole pairs as shown on the left-hand side of FIG.5 and thus put the insulator IS1 itself into a conductive state. Thewavelength λ1 of the laser beam L1 that is necessary for achieving sucha state has to satisfy the equation λ1<hc/Eg, where h is Planck'sconstant and c is the speed of light. If the above-described insulatorIS1 is silicon dioxide (SiO₂) and that energy gap Eg is 9 (eV), forexample, the longest wavelength λm of the laser beam L1 having energy ofat least that energy gap is given by:λm=hc/Eg=137 (nm)

As shown in the right-hand portion of FIG. 5, there are local levels LL1and LL2 in the insulator IS1 that immobilize electrons and holes (seethe left-hand portion of FIG. 6), and electrons e2 and holes HL2 thatare immobilized by these have a large effect on the charged state of theinsulator IS1. The electrons e2 and holes HL2 that have been immobilizedby these local levels LL1 and LL2 can be made to migrate by causing themto absorb energy from laser beams L2 and L3 that are shone thereon asshown in FIG. 5. This makes it possible to reduce local charges thatcause immobilization to the local potential, thus making it possible toreduce local potential differences. More specifically, the immobilizedelectrons e2 can be made to migrate if they are irradiated with a laserbeam (electromagnetic waves) L2 having at least the energy difference Eebetween the local level LL1 at which the electrons e2 are immobilizedand the lower bound of the conduction band Ec, as shown in FIG. 6. Thewavelength λ2 of the laser beam L2 that is necessary for achieving sucha state must satisfy the condition: λ2<hc/Ee. Similarly, the immobilizedholes HL2 can be made to migrate if they are irradiated with a laserbeam (electromagnetic waves) L3 having at least the upper bound of thevalence band Ev. The wavelength λ3 of the laser beam L3 that isnecessary for achieving such a state must satisfy the condition:λ3<hc/Eb. As the wavelength of a laser beam shortens, both the size andcost of the apparatus increase. However, since λ1<λ2 and λ1<λ3 areeffective in general, it is possible to constrain the cost and size ofthe laser beam irradiation device 120 by reducing the local charge ofthe insulating body IS1 through above-mentioned migration of theimmobilized electrons e2 and holes HL2 as long as there are no problemswith the capability of the apparatus. This makes it possible toimplement an apparatus that is much more cost-effective and compact.

Third Embodiment

The method of this embodiment reduces the charge of the insulator in thevicinity of each boundary between an insulator and a conductor or in thevicinity of an insulator and a semiconductor. Simply using theinspection method of this third embodiment reduces local potentialdifferences in the vicinities of the above-described boundaries, thusmaking it possible to suppress distortion and contrast deterioration ofthe detected image of the secondary beam, with no need of making thecharge location of the insulator conductive. If the insulator ispositively charged, for example, electrons could migrate (be implanted)from the metal or semiconductor to the insulator, to neutralize thatpositive charge. In an example shown in FIG. 7, the irradiation of alaser beam L4 onto a boundary C3 between a metal layer ML and aninsulator IS2 causes electrons to migrate from the metal layer ML to theinsulator IS2.

The energy bands at the connection between the metal and the insulatorare shown in FIG. 8. A laser beam (electromagnetic waves) L4 having anenergy of at least the energy eφ of the contact potential barrier of theboundary between the metal layer ML and the insulator IS2 could be shoneonto this boundary C3 to cause an electron e4 within the metal layer MLto migrate to the insulator IS2. The wavelength λ4 of the laser beam L4that is necessary for achieving such a state must satisfy the condition:λ4<hc/Eb. In this case, if the conductor is silicon (Si), the insulatoris silicon dioxide (SiO₂), and the potential barrier at the Si—SiO₂contact region is Eb=3.5 (eV), the longest wavelength λm of the laserbeam L4 having energy of at least that potential barrier is given by:λm=hc/Eg=354 (nm)

In general, since λ1<λ4, it is possible to constrain the cost and sizeof the laser beam irradiation device 120 by neutralizing the positivecharges of the insulating body IS2 in the vicinity of theabove-described boundaries, provided there are no problems with thecapability of the apparatus. This makes it possible to provide anapparatus that is much more cost-effective and compact.

Note that the laser beam irradiation device 120 is used in thisembodiment for reducing local potential differences in the surface ofthe specimen S, but any other device for irradiating electromagneticwaves could be used therefore, such as a device that uses X-rays or anultraviolet lamp in accordance with factors such as the properties orshape of the specimen to be inspected.

Fourth Embodiment

A block diagram of the basic configuration of a substrate inspectionapparatus in accordance with a fourth embodiment of the presentinvention is shown in FIG. 9. A substrate inspection apparatus 2 shownin this figure is characterized in that it comprises additional electronbeam irradiation devices 130 and 140 to generate the electron beamsE_(B1) and E_(B2), respectively, for irradiating the specimen S, a CADdata storage device 68, an electron beam irradiation condition processor66, and an electron beam irradiation condition storage device 64. Therest of the configuration of the substrate inspection apparatus 2 issubstantially the same as that of the substrate inspection apparatus 1of FIG. 1.

The electron beam irradiation device 130 is disposed at a position suchthat an arbitrary point within the exposure region of the specimen Sfirst passes through an intersection IP₁ between the optical axisA_(EB1) of the electron beam from the electron beam irradiation device130 itself and the surface of the specimen S, before the intersectionIP₀ between the optical axis As of the secondary optical system and thesurface of the specimen S, with respect to the stage scan directionD_(SS) during the inspection of the specimen surface. Similarly, theelectron beam irradiation device 140 is disposed at a position such thatan arbitrary point within the exposure region of the specimen S firstpasses through an intersection IP₂ between the optical axis A_(EB2) ofthe electron beam irradiation device 140 itself and the surface of thespecimen S, before the above-described intersection IP₁. Such adisposition makes it possible to reduce potential differences in thespecimen surface by the electron beam irradiation devices 130 and 140before the secondary electronic image of the specimen surface isobtained by the electron detector 30. The description of this embodimentbelow takes as an example in which the specimen surface moves insequence through the intersection IP₂, the intersection IP₁, and theintersection IP₀.

The electron beam irradiation device 130 includes a W filament 132, aWehnelt electrode 134, an anode 136 and an electron beam controller 138.The W filament 132 has a coil shape and generates the electron beamE_(B1). The W filament 132 is disposed so as to shine the electron beamE_(B1) of this embodiment perpendicularly onto the surface of thespecimen S. The Wehnelt electrode 134 controls the rate of emission ofthe electron beam EB1 from the W filament 132. The anode 136 extractsthe electron beam EB1 emitted from the W filament 132. The W filament132, the Wehnelt electrode 134, and the anode 136 are all connected toan electron beam controller 138 and are controlled thereby.

Similarly, the electron beam irradiation device 140 includes a Wfilament 142 for generating the electron beam EB2, a Wehnelt electrode144, an anode 146 and an electron beam controller 148, with thesestructural elements being disposed in a similar manner and exhibitingsimilar functions as the W filament 132, the Wehnelt electrode 134, andthe anode 136 of the electron beam irradiation device 130. Furtherdescription of those structural elements is therefore omitted.

The CAD data storage device 68 stores data on layout patterns of thespecimen S of the object to be inspected and data on the electricalcharacteristics of each layout pattern. The electron beam irradiationcondition processor 66 uses the data stored in the CAD data storagedevice 68 to pre-calculate irradiation conditions for the primary beamBp and the electron beams E_(B1) and E_(B2) in advance of theinspection. The electron beam irradiation condition storage device 64stores the results of the calculations of the electron beam irradiationcondition processor 66.

The description now turns to the principles of the substrate inspectionmethod of this embodiment.

One way of solving the problems of distortion and contrast deteriorationin the detected secondary beam image is to reduce the potentialgradients in the specimen surface that are the cause thereof. Asdescribed with reference to the example of FIG. 28, the primary beam Bpcould irradiate the surface of the specimen S with the insulatingportion 214 under negative charging conditions, to reduce the potentialdifference between the metal wiring 212 and the insulating portion 214.A contact potential is always formed in the contact region between ametal and an insulator, so that the insulator is in a positive potentialstate of several volts with respect to the metal, when the primary beamBp is not shone thereon. In such a case, the primary beam Bp could beshone onto the insulator under a condition in which the insulator isnegatively charged.

The condition in which the insulator is negatively charged could be onein which a primary beam irradiates the insulator with incident energysuch that the total secondary electron emission ratio σ from theinsulator is 1 or less, in which case, if the insulator 214 shown inFIG. 28 is SiO₂, the value of the incident energy is at leastapproximately 1 keV or no more than approximately 50 eV, as shown inFIG. 10. If the quantity of secondary electrons (in this case, secondaryelectrons are used in a broad sense so as to include reflected electronsand backscattered electrons) is increased, the signal level for formingthe image will increase, which will shorten the time until an image isformed. In other words, this makes it possible to shorten the inspectiontime. Conventional methods have been used in which this total secondaryelectron emission ratio δ is set to at least 1, from consideration ofinspection throughput. With this embodiment of the invention, however,the insulating portions are negatively charged by setting the totalsecondary electron emission ratio δ to less than 1, in contradiction toconventional technique. This makes it possible to increase the accuracyof the detected image. Hereinafter, this process of irradiating theinsulator with the electron beam under negative charging conditions iscalled Process 1.

Taking the specimen S shown in FIG. 28 as an example, theabove-described Process 1 gradually reduces the potential of theinsulating portion 214 from an initial state at which it is at a fewpositive volts with respect to the metal wiring 212, until it is at thesame potential as the metal wiring 212, as shown in FIG. 11. Thesecondary beam trajectory Bsp2 and Bsp4 in this state are the same asthe electron beam trajectories TJ_(IP2) and TJ_(IP4) that are ideal foraccurate mapping projection. As a result, it is possible to obtain aninspection image with no distortion or contrast deterioration.

However, executing this process of reducing the potential differences ofthe surface of the specimen S as far as possible before the process ofobtaining the inspection image takes time to even out the potentialdifferences of the specimen surface, causing the inspection throughputto deteriorate. In this case, as will be described later, the use of aseparate electron beam from the primary beam Bp that is used forobservation makes it possible to solve the problem of throughputdeterioration, with substantially no wait time, by using the separateelectron beam to pre-irradiate the inspection region of the surface ofthe specimen S, in parallel with the irradiation by the primary beam Bpand immediately before the irradiation by the primary beam Bp, to reducepotential differences in that region to as small as possible. With thisembodiment, the additional electron beam irradiation devices 130 and 140are used to perform pre-processing by the electron beams E_(B1) andE_(B2). This pre-processing is called Process 2 below.

There is a problem with Process 1 and Process 2, concerning a differencein the dosage of the electron beams necessary for minimizing surfacepotential differences, which is created by the layout pattern andelectrical characteristic of the metal wiring 212 and the insulatingportion 214 in the surface of the specimen S. If the metal wiring 212takes up a large proportion of the area, a large quantity of electronswill leak from the insulating portion 214 to the metal wiring 212,making it necessary to irradiate a large quantity of the electron beamsuntil the surface potential differences are minimized. In addition,differences are generated in the quantities of electrons leaking fromthe insulating portion 214, depending on whether or not the metal wiring212 and the substrate are conductive to each other. Such problems causeimage distortion and focus shift due to non-uniformity of the surfacepotentials within the same field of view during the capture of thesurface of the specimen S. One way to avoid such problems would be toadjust a specific irradiation condition that applies when the insulatingportion 214 is under a negative charging condition, in accordance withthe above-described layout pattern and electrical characteristics, suchas the total current magnitude for the electron beam per unit surfacearea of the specimen S or the energy incident thereon. Since there is alarge leakage of electrons from the insulating portion 214 in regionswith a large conductive to the substrate, it would be good to increasethe total current magnitude for the electron beam per unit surface areaof the specimen S to more than in other regions, or irradiate theelectron beam with incident energy such that the total secondaryelectron emission ratio σ is smaller.

It would also be effective to make the surface potentials of thespecimen more even before Process 1, even if the electron beam is shonethereon under conditions such that the insulator is positively charged.Such pre-processing is called Process 3 hereinafter.

A problem that occurs if the primary beam Bp irradiates the surface ofthe specimen S too much in the above-described negative chargingcondition is illustrated in FIG. 12. If the primary beam Bp hasirradiated the insulating portion 214 excessively, the insulatingportion 214 will become negatively charged and could even acquire apotential that is more negative than the metal wiring 212, as shown inthe figure. Other cases could be considered within the same image whenthe surface of the specimen S is imaged, even when a leveling of surfacepotentials has been achieved in other regions, such as the insulatingportion 214 is in a negatively charged state dependent on the layoutpattern and electrical characteristics of the region shown in FIG. 12,or uniform surface potential state has collapsed. In such a case too,local potential gradients that are not parallel to the surface of thespecimen S are created in the vicinity of the boundary 216 between themetal wiring 212 and the insulating portion 214, in a similar manner tothat shown in FIG. 28 with the positive charge. When the secondaryelectrons emitted from the point P₂ within the metal wiring 212 in thevicinity of the boundary and the point P₄ within the insulating portionare controlled by the secondary optical system 20 to form an image onthe MCP detector 31, these potential gradients will exert aninappropriate deflection effect, making them deviate from the electronbeam trajectories TJ_(IP2) and TJ_(IP4) that are ideal for accuratemapping projection and curve as shown by the trajectories TJ_(RP6) andTJ_(RP8). In such a case, the primary beam Bp pre-irradiates the surfaceof the specimen S when the insulating portion 214 is under a positivecharging condition, before the processing of Process 1, so that regionsthat are likely to become negatively charged in Process 1 (such asregions in which there is not much of metal wiring 212 or regions inwhich the metal wiring 212 is conductive with the substrate) will becomepositively charged before the other regions, during Process 3. Suchprocessing makes it possible to avoid the problem of local variations insurface potential that are dependent on the pattern layout or electricalcharacteristics of the surface of the specimen S, when an image of thesurface of the specimen S is picked up in Process 1.

The substrate inspection apparatus 2 of FIG. 9 operates in accordancewith the above inspection principles. The description now turns tospecific details of the operation of the substrate inspection apparatus2.

Before the inspection, the electron beam irradiation condition processor66 first extracts layout pattern data and electrical characteristic datafor the specimen S from the CAD data storage device 68. It calculatesthe irradiation conditions for the primary beam Bp and the electronbeams E_(B1) and E_(B2) at each position of the stage 43 when thelocation that is the object of observation on the specimen S, in otherwords, the exposure region is positioned at the intersection IP₀ betweenthe optical axis As and the surface of the specimen S, to ensure thateither the surface potentials within the exposure region are uniform orany potential differences in the surface are minimized. The results ofthese calculations are stored in the electron beam irradiation conditionstorage device 64.

After the inspection has started, the host computer 60 extracts theirradiation conditions for the electron beam EB2, the electron beam EB1,and the primary beam Bp for each stage position, while referencing thecurrent position information of the stage 43 that is supplied from thestage driver 47. In addition, the host computer 60 transmits thoseirradiation conditions to an electron beam controller 148, the electronbeam controller 138, the electron gun controller 16, and the multi-stagequadrupole lens controller 17 to control the electron beam irradiationdevice 140, the electron beam irradiation device 130, and the primaryoptical system 10, respectively, and thus adjust the irradiationconditions of the electron beam EB2, the electron beam E_(B1), and theprimary beam Bp. The following five cases of these irradiationconditions can be considered, by way of example, as shown in FIG. 13:

-   Case 1: The primary beam Bp irradiates the insulator under negative    charging conditions. The electron beams E_(B1) and E_(B2) are not    emitted.-   Case 2: The primary beam Bp irradiates the insulator under negative    charging conditions. The electron beam E_(B1) irradiates the    insulator under negative charging conditions. The electron beam    E_(B2) is not emitted.-   Case 3: The primary beam Bp irradiates the insulator under negative    charging conditions. The electron beam E_(B1) irradiates the    insulator under positive charging conditions. The electron beam    E_(B2) is not emitted.-   Case 4: The primary beam Bp irradiates the insulator under negative    charging conditions. The electron beam E_(B1) irradiates the    insulator under negative charging conditions. The electron beam    E_(B2) irradiates the insulator under positive charging conditions.-   Case 5: The primary beam Bp irradiates the insulator under negative    charging conditions. The electron beam E_(B1) irradiates the    insulator under positive charging conditions. The electron beam    E_(B2) irradiates the insulator under negative charging conditions.

In this manner, it is possible to obtain a highly accurate inspectionimage, with no image distortion or focus shift, by inspecting thespecimen S under the optimal conditions for leveling the specimensurface potentials that are adopted by the electron beam irradiationcondition processor 66.

In the description above, two additional electron beam irradiationdevices are used for leveling the surface potentials, but the presentinvention is not limited thereto and thus the above-described methodcould be employed in a configuration that comprises just one additionalelectron beam irradiation device, such as in a substrate inspectionapparatus 3 shown in FIG. 14 by way of example, or a configuration thatcomprises three or more additional electron beam irradiation devices(not shown in the figures).

The description now turns to fifth to eighth embodiments of the presentinvention, with reference to FIGS. 15 to 26. First of all, theinspection principle on which the embodiments below depend will bedescribed with reference to FIGS. 15 and 16. Note that in the followingembodiments the term “a secondary electron” is to be used in a narrowsense so as to exclude a reflected electron (and a backscatteredelectron).

To avoid the effects of potential gradients on the specimen surface andimplement highly accurate defect detection, it is also possible to usereflected electrons that have higher emission energy than secondaryelectrons (also called elastic scattering electrons) for the imaging.FIG. 15 shows the energy distributions of electrons emitted from thesubstrate by incidence of the primary beam thereon. As shown in thisgraph, the emission energy distribution of the electrons exhibits thelargest peak in the region of a few eV or less. With a conventionalinspection apparatus, to amplify the magnitude of the detection signal,the secondary optical system is controlled in such a manner thatsecondary electrons having this emission energy of a few eV or less areimaged on the detection surface of the detector. In contrast thereto,since reflected electrons within the backscattered electrons havesubstantially the same energy as the incident energy of the primarybeam, the use of these reflected electrons in the imaging make itdifficult for the above-described potential gradients to have anyeffect, and ensures the passage of electron beam trajectories that areideal for accurate mapping projection, such as the trajectories TJ_(IP2)and TJ_(IP4) shown by way of example in FIG. 28. This makes it possibleto avoid the problems of distortion and contrast deterioration in thesecondary beam inspection image. Note that FIG. 15 shows the energydistribution of emission electrons when the incident energy of theprimary beam is 500 eV and when it is 1000 eV, but the present inventionis not limited to such high incident energies and can equally well beapplied when the incident energy of the primary beam is low, making itpossible to avoid distortion and contrast deterioration of theinspection image by the use of imaging of reflected electrons having anemission energy that is higher than that of the secondary electrons.

In addition, even with defect inspection using imaging of thesereflected electrons, the optical conditions of the inspection apparatuscould be set to ensure that the above-described three characteristicsare ideal, to improve the inspection capabilities.

However, it is difficult in the prior art to implement conditions thatenable optimization of all three of the above characteristics, such asthe optimal incident energy of the primary beam. The relationships shownschematically in FIG. 16 are of the primary beam incident energy and thedistortion (L1) and S/N (L2) ratio of the detected image duringobservation of an integrated circuit on the surface of a wafer that hasbeen imaged by using reflected electrons. From the distortion viewpoint,since the emission energy of reflected electrons increases as theincident energy increases, the effects due to local potentialdifferences on the specimen surface become less obvious and sodistortion is reduced to a certain degree.

However, from the S/N viewpoint, the incident electrons penetrate intothe deeper locations of the specimen in regions in which incident energyis high, so that the quantity of emitted reflected electrons is reducedin such locations and thus the signal magnitude that contributes to theimaging of the specimen surface (corresponding to the S/N ratio) isreduced by that amount. The S/N ratio of the detected image is thereforereduced. Note that the actual quantities of reflected electrons andbackscattered electrons that are emitted from the specimen in regions inwhich the incident energy is low are amplified, but the signal magnitude(the N part of the S/N ratio) of electrons that arrive at the detectionsurface of the detector but do not contribute to the imaging (electronshaving lower energy levels than those of the reflected electrons, on theorder of only a few to several hundred eV) is also amplified by anamplification ratio for noise (N) that is greater than the amplificationratio for the signal (S), so the S/N ratio is effectively reduced.

The above reasoning shows that it is substantially impossible with theconventional inspection apparatus to implement incident energy for theprimary beam such that distortion is minimized but the S/N ratio ismaximized. If the characteristic that renders the material contrastmaximized is considered as well, it becomes even more impossible toimplement incident energy for the primary beam.

Embodiments of the present invention enable quantitative searching ofconditions for obtaining the optimal image, by using estimated valuesthat assess the above-described three characteristics. Some of theseembodiments are described below with reference to the accompanyingfigures.

Fifth Embodiment

A block diagram of the basic configuration of a substrate inspectionapparatus in accordance with a fifth embodiment of the present inventionis shown in FIG. 17. Instead of the host computer 60 of the substrateinspection apparatus 1 shown in FIG. 1 by way of example, a substrateinspection apparatus 4 shown in FIG. 17 comprises a host computer 61that calculates primary beam incident energy conditions for obtainingthe optimal specimen surface images for inspection. The rest of theconfiguration of the substrate inspection apparatus 4 of this embodimentis substantially the same as the substrate inspection apparatus 1 ofFIG. 1, except for the particular provision of a storage device MR2 andthe fact that the laser beam irradiation device 120 is not provided.

In addition to storing the image data processed by the host computer 61,the storage device MR2 stores correspondences between the overall imageestimated value M(n) and the stage applied voltage Vr, calculated by thehost computer 61. The overall image estimated value M(n) and the stageapplied voltage Vr will be discussed later.

The description now turns to a more specific configuration of the hostcomputer 61 of the substrate inspection apparatus 4, with reference tothe block diagram of FIG. 18. As shown in the figure, the host computer61 includes an image optimization condition inspection condition inputsection 164, an image optimization condition inspection instructionsection 162, an overall image estimated value calculator 166, and animage display processor 168.

The host computer 61 defines an overall image estimated value M(n) thatis a value for evaluating distortion, S/N ratio, and contrast of thedetected image in a comprehensive manner, and calculates primary beamincident energy conditions for obtaining the specimen surface image thatis best for the inspection, by searching for conditions that maximizethis M(n). The operation of the host computer 61 will now be describedwith reference to the flowchart of FIG. 19. Note that when it comes toinspecting the optimal incident energy conditions with this embodiment,the incident energy will be affected by changes in the stage appliedvoltage.

As shown in FIG. 19, a lower limit V₀ and an upper limit V_(e) of aninspection range V₀ to V_(e) of the stage applied voltage, a number ofdivisions N for that inspection range, and also weighting coefficientsk_(d), k_(s), and k_(c) corresponding to three image evaluation items(in other words, distortion, S/N ratio, and materials contrast) is firstinputted to the image optimization condition input section 164 (stepS1). These three weighting coefficients k_(d), k_(s), and k_(c) are setso as to achieve what is thought to be the optimal detected image foreach inspection. The image optimization condition inspection instructionsection 164 then sets n to zero, calculates the stage applied voltageoptimal condition inspection resolution V_(d)=(V_(e)−V₀)/N (step S2),and outputs a control signal to the stage voltage controller 51 suchthat a stage applied voltage of Vr=V₀+nVd (in this case, n=0 so Vr=V₀)is applied to the stage 43 (step S3). Control signals are also suppliedto the various mapping projection optical system controllers 52 to 57 toensure that the various mapping optical system control voltages orcurrents corresponding to this stage applied voltage Vr are set (stepS4), an image of the surface of the specimen S is obtained, and thecorresponding image data is stored in the storage device MR2 (step S5).After the image of the specimen surface has been obtained, the imageoptimization condition inspection instruction section 164 outputs acontrol signal indicating that the image of the specimen surface hasbeen obtained to the overall image estimated value calculator 166. Onreceiving that signal, the overall image estimated value calculator 166extracts the specimen surface image from the storage device MR2,calculates an image distortion estimated value M_(d), an image S/Nestimated value M_(s), and an image materials contrast estimated valueM_(c) based on that image, and also calculates the overall imageestimated value M(n) (=k_(d)M_(d)+k_(s)M_(s)+k_(c)M_(c)) and stores itin the storage device MR2 (step S6). This estimated value calculationmethod is set beforehand to give an image that is suitable forinspection with large values of the image distortion estimated valueM_(d), image S/N estimated value M_(s), and image materials contrastestimated value M_(c). When the image optimization condition inspectioninstruction section 164 calculates the overall image estimated valueM(n), the system determines whether or not the inspection has ended bycomparing n and N (step S7). If n<N, it determines that the inspectionhas not ended and the image optimization condition inspectioninstruction section 164 substitutes n+1 into n (step S8), and thesequence of steps S3 to S7 is repeated. When n reaches N, it determinesthat the inspection has ended (step S7). The image optimizationcondition inspection instruction section 164 extracts the largestestimated value from the overall image estimated values M(0) to M(N),determines that the stage applied voltage Vr that was obtained at thatlargest image estimated value is the optimal stage applied voltagecondition, and also determines that the inspection image obtained atthat optimal stage applied voltage condition is the optimal conditionimage, then stores those values in the storage device MR2 (step S9) andends the primary beam incident energy optimal condition inspectionsequence.

In addition, the host computer 61 uses known image processing techniqueson the optimal condition image obtained by the above-described sequence,to detect whether or not there are defects in the specimen S and, if adefect is detected, determines details such as the size and propertiesof that defect and outputs that information.

According to the thus-configured embodiment, there is calculated theimage distortion estimated value M_(d), image S/N estimated value M_(s),and image materials contrast M_(c) which are estimated values based onnumerical values of distortion, S/N, and contrast evaluationcharacteristics; also set weighting coefficients k_(d), k_(s), and k_(c)that are compatible with the object to be inspected and is calculatedthe overall image estimated value M(n)(=k_(d)M_(d)+k_(s)M_(s)+k_(c)M_(c)). Thus, it makes it possible toacquire primary beam incident energy conditions at which the optimalsubstrate surface image is obtained. Since this ensures that onlyreflected electrons (which have substantially the same energy afteremission as the incident energy of the primary beam) are detected, thismakes it possible to avoid the effects of local potential differences inthe specimen surface, thus making it possible to obtain an inspectionimage that has little distortion and also a superior contrast. As aresult, it is possible to detect the substrate surface image with a highlevel of sensitivity.

Sixth Embodiment

A block diagram of the basic configuration of a substrate inspectionapparatus in accordance with a sixth embodiment of the present inventionis shown in FIG. 20. In addition to the configuration shown in FIG. 17,a substrate inspection apparatus 5 comprises a Wien filter 81 that isseparate from the Wien filter 41 that separates the primary beam Bp andthe secondary beam Bs, a controller 83 therefor, noise electron trapelectrodes 72 and 84, and controllers 73 and 85 for these noise electrontrap electrodes. The Wien filter 81 is disposed between the fourth lens24 and the MCP detector 31 within the secondary optical system. The Wienfilters 41 and 81 are controlled by the corresponding Wien filtercontrollers 53 and 83 to ensure that reflected electrons, which have ahigh emission energy in comparison with the secondary electrons and thusmake it possible to avoid distortion and contrast deterioration of thedetected image, are passed through to form an image on the MCP detector31. The noise electron trap electrode 72 is disposed between the Wienfilter 41 and the second lens 22 and the noise electron trap electrode84 is disposed between the Wien filter 81 and the MCP detector 31. Therest of the configuration of the substrate inspection apparatus 5 issubstantially the same as that of the substrate inspection apparatus 4of FIG. 17.

When reflected electrons are used for imaging the specimen surface,these reflected electrons have an emission magnitude that is smallerthan that of the secondary electrons, but the energy spread is wider.Since that means that the proportion of noise electrons that arrive atthe MCP detector 31 is large in comparison with the quantity ofelectrons used in the original imaging, a problem arises in that the S/Nratio of the detected image is large and thus deterioration occurs.

To solve such a problem, the Wien filter 41 of this embodiment also hasthe function of a filter for removing noise component electrons. Inaddition, the Wien filter 81 is disposed between the fourth lens 24 andthe MCP detector 31. These Wien filters 41 and 81 are designed to causethe deflection of noise component electrons e_(N2) and e_(N4) so thatthey cannot arrive at the MCP detector 31. It should be noted, however,that the deflected noise component electrons e_(N2) and e_(N4)eventually irradiate the electrodes of the secondary optical system,contaminate the interior of the secondary optical system, and have anadverse effect on the electrical fields therein, leading to results thatare not desirable to ignore. With this embodiment, positive voltages areapplied by the noise electron trap electrode controllers 73 and 85 tothe corresponding noise electron trap electrodes 72 and 84, thisimmobilizes the deflected noise component electrons in the noiseelectron trap electrodes 72 and 84, preventing contamination within thesecondary optical system.

In this manner, since this embodiment is provided with the Wien filters41 and 81 that deflect the noise component electrons e_(N2) and e_(N4)and the noise electron trap electrodes 72 and 84 that immobilize thethus-deflected noise component electrons e_(N2) and e_(N4), reflectedelectrons that have a high emission energy in comparison with thesecondary electrons thus pass through the secondary optical system 20 asthe secondary beam Bs and are imaged by the MCP detector 31, whereasnoise electrons that are not these reflected electrons can be preventedfrom arriving at the MCP detector 31, it is possible to preventdistortion and contrast deterioration in the secondary electron beaminspection image. Note that the installation locations and electron trapelectrodes do not necessarily conform to this embodiment. For example,if the Wien filter 41 alone can separate the primary beam Bp and thesecondary beam Bs and also separate the reflected electrons thatcontribute to the imaging and the other noise electrons, it is notnecessary to provide an additional Wien filter.

Seventh Embodiment

A block diagram of the basic configuration of a substrate inspectionapparatus in accordance with a seventh embodiment of the presentinvention is shown in FIG. 21. In addition to the configuration shown inFIG. 17, a substrate inspection apparatus 6 shown in FIG. 21 comprises anoise electron shield electrode 88, a noise electron shield electrodecontroller 89, a noise electron trap electrode 86, and a noise electrontrap electrode controller 87. The noise electron shield electrode 88 isprovided with a circular hole in the center that permits the secondarybeam Bs to pass through, as shown in a perspective view of FIG. 22together with a plan view and section there through of FIGS. 23A and23B, it is disposed between the fourth lens 24 and the MCP detector 31within the secondary optical system 20, and it is connected to the noiseelectron shield electrode controller 89 and a negative voltage isapplied thereto. The value of this negative voltage is set to a valuethat enables the noise electron shield electrode 88 to excite ashielding electrical field to prevent the passage through the circularhole of the noise electron shield electrode 88 by noise componentelectrons e_(N6) emitted from the specimen S at an energy below theenergy of electrons that are used for imaging within the secondary beamBs. The noise electron trap electrode 86 is disposed between the fourthlens 24 and the noise electron shield electrode 88, and is connected tothe noise electron trap electrode controller 87 and a positive voltageis applied thereto. This ensures that noise component electrons e_(N6)that have been deflected by the shield electrical field excited by thenoise electron shield electrode 88 are immobilized in the noise electrontrap electrode 86, preventing contamination of the secondary opticalsystem 20. This embodiment is suitable for cases in which emittedelectrons having substantially the same energy as the energy incident onthe specimen S by the primary beam Bp, in other words, reflectedelectrons, are used for imaging. Note that the installation locationsand numbers of the noise electron shield electrode 88 and the noiseelectron trap electrode 86 do not necessarily conform to theconfiguration shown in FIG. 21, in a similar manner to theabove-described sixth embodiment. In addition, the noise electron shieldelectrode 88 of this embodiment has been described as having a circularhole shape, but the shape of the noise electron shield electrode is notlimited thereto and thus it could have a grid (mesh) shape formed in alattice pattern, as shown by way of example as an electrode 98 in aperspective view of FIG. 24 together with a plan view and section therethrough of FIGS. 25A and 25B.

Eighth Embodiment

A block diagram of the basic configuration of a substrate inspectionapparatus in accordance with an eighth embodiment of the presentinvention is shown in FIG. 26. In addition to the configuration shown inFIG. 17, a substrate inspection apparatus 7 shown in FIG. 26 comprises anoise electron shield electrode 108 and a noise electron shieldelectrode controller 109. The noise electron shield electrode 108 is anelectrode having a circular hole shape disposed between the specimen Sand the secondary optical system 20 (see FIGS. 22 and 12), it isconnected to the noise electron shield electrode controller 109 and hasa negative voltage applied thereto. The value of this negative voltageis set to a value that enables the noise electron shield electrode 108to excite a shielding electrical field to prevent the passage throughthe circular hole of the noise electron shield electrode 108 by noisecomponent electrons e_(N8) emitted from the specimen S at an energybelow the energy of electrons that are used for imaging within thesecondary beam Bs, in a similar manner to the above-described seventhembodiment. Since this prevents the noise component electrons e_(N8)from arriving at the MCP detector 31, it makes it possible to reduce thenoise component at the MCP detector 31.

The disposition of the noise electron shield electrode 108 between thespecimen S and the secondary optical system 20 in this manner has twofurther advantages, as follows:

-   1) It makes it possible to prevent contamination of the secondary    optical system due to noise component electrons, without providing a    noise component electron trap electrode such as that of the    above-described sixth and seventh embodiments.-   2) It reduces local charging of the specimen surface by    redistributing the noise component electrons that have been turned    back by the noise electron shield electrode 108 towards positively    charged locations on the surface of the specimen S, such as the    insulator regions.

This reduces local potential differences of the specimen surface, makingit possible to control distortion and contrast deterioration of thedetected image. Note that the shape of the noise electron shieldelectrode 108 is not limited to a circular hole shape and thus it issimilar to the above-described seventh embodiment in that it could havethe grid (mesh) shape shown in FIGS. 24, 25A, and 25B, by way ofexample.

Method of Manufacturing Semiconductor Device

Since the use of above-described substrate inspection process during theprocess of manufacturing a semiconductor device makes it possible toinspect substrates with a high level of accuracy, it makes it possibleto manufacture semiconductor device at a higher yield.

The present invention has been described above with reference toembodiments thereof, but the present invention is not limited to thoseembodiments and it should be clear to those skilled in the art thatvarious modifications are possible within the scope thereof. Forexample, the above embodiments were described as relating to a substrateinspection apparatus that uses a stage-scanning method, but the presentinvention could of course be applied to a substrate inspection apparatususing a deflector for a beam-scanning method, and even to a substrateinspection apparatus that comprises both of these scanning methods.

1. A substrate inspection apparatus comprising: an electron beamirradiation device which emits an electron beam and causes the electronbeam to irradiate a substrate to be inspected as a primary beam; anelectron beam detector which detects at least one of a secondaryelectron, a reflected electron and a backscattered electron that aregenerated from the substrate that has been irradiated by the electronbeam, and which outputs a signal that forms a one-dimensional ortwo-dimensional image of a surface of the substrate; a mappingprojection optical system which causes imaging of at least one of thesecondary electron, the reflected electron and the backscatteredelectron on said electron beam detector as a secondary beam; and anelectromagnetic wave irradiation device which provides a location on thesurface of the substrate at which the secondary beam is generated, withenergy to thereby migrate a local charge within the substrate bygenerating an electromagnetic wave and causing the electromagnetic waveto irradiate the location.
 2. The substrate inspection apparatusaccording to claim 1, wherein said electromagnetic wave irradiationdevice causes the electromagnetic wave to irradiate the location on thesurface of the substrate so that a first area on the surface of thesubstrate irradiated by the electromagnetic wave overlaps a second areaon the surface of the substrate irradiated by the primary beam.
 3. Thesubstrate inspection apparatus according to claim 1, wherein saidelectromagnetic wave irradiation device causes the electromagnetic waveto irradiate the location on the surface of the substrate substantiallysimultaneously with the irradiation of the primary beam.
 4. A substrateinspection apparatus comprising: an electron beam irradiation devicewhich emits an electron beam and causes the electron beam to irradiate asubstrate to be inspected as a primary beam; an electron beam detectorwhich detects at least one of a secondary electron, a reflected electronand a backscattered electron that are generated from the substrate thathas been irradiated by the electron beam, and which outputs a signalthat forms a one-dimensional or two-dimensional image of a surface ofthe substrate; a mapping projection optical system which causes imagingof at least one of the secondary electron, the reflected electron andthe backscattered electron on said electron beam detector as a secondarybeam; and an electromagnetic wave irradiation device which generates anelectromagnetic wave and causes the electromagnetic wave to irradiate alocation on the surface of the substrate at which the secondary beam isgenerated, wherein a wavelength of the electromagnetic wave is definedon the basis of a band gap or localized level of a material of thesurface of the substrate.
 5. A substrate inspection apparatuscomprising: an electron beam irradiation device which emits an electronbeam and causes the electron beam to irradiate a substrate to beinspected as a primary beam; an electron beam detector which detects atleast one of a secondary electron, a reflected electron and abackscattered electron that are generated from the substrate that hasbeen irradiated by the electron beam, and which outputs a signal thatforms a one-dimensional or two-dimensional image of a surface of thesubstrate; a mapping projection optical system which causes imaging ofat least one of the secondary electron, the reflected electron and thebackscattered electron on said electron beam detector as a secondarybeam; and an electromagnetic wave irradiation device which generates anelectromagnetic wave and causes the electromagnetic wave to irradiate alocation on the surface of the substrate at which the secondary beam isgenerated, wherein the substrate has a surface layer formed of aplurality of different materials contacting each other at a contactregion in the surface layer, and a wavelength of the electromagneticwave is defined on the basis of a potential barrier at the contactregion.
 6. A substrate inspection method comprising: emitting anelectron beam and causing the electron beam to irradiate a substrate tobe inspected as a primary beam; projecting at least one of a secondaryelectron, a reflected electron and a backscattered electron that aregenerated from the substrate that has been irradiated by the electronbeam, as a secondary beam to cause imaging of the secondary beam;detecting an image caused by said imaging of the secondary beam andoutputting a signal to form a one-dimensional or two-dimensional imageof a surface of the substrate; and providing a location on the surfaceof the substrate at which the secondary beam is generated, with energyto thereby migrate a local charge within the substrate by irradiatingthe location with an electromagnetic wave.
 7. The substrate inspectionmethod according to claim 6, wherein a first area on the surface of thesubstrate irradiated by the electromagnetic wave overlaps a second areaon the surface of the substrate irradiated by the primary beam.
 8. Thesubstrate inspection method according to claim 6, wherein theirradiation of the electromagnetic wave is implemented substantiallysimultaneously with the irradiation of the primary beam.
 9. A substrateinspection method comprising: emitting an electron beam and causing theelectron beam to irradiate a substrate to be inspected as a primarybeam; projecting at least one of a secondary electron, a reflectedelectron, and a backscattered electron that are generated from thesubstrate that has been irradiated by the electron beam, as a secondarybeam to cause imaging of the secondary beam; detecting an image causedby said imaging of the secondary beam and outputting a signal to form aone-dimensional or two-dimensional image of a surface of the substrate;and generating an electromagnetic wave and causing the electromagneticwave to irradiate a location on the surface of the substrate at whichthe secondary beam is generated; wherein a wavelength of theelectromagnetic wave is defined on the basis of a band gap or localizedlevel of a material of the surface of the substrate.
 10. A substrateinspection method comprising: emitting an electron beam and causing theelectron beam to irradiate a substrate to be inspected as a primarybeam, the substrate having a surface layer formed of a plurality ofdifferent materials contacting each other; projecting at least one of asecondary electron, a reflected electron, and a backscattered electronthat are generated from the substrate that has been irradiated by theelectron bean, as a secondary beam to cause imaging of the secondarybeam; detecting an image caused by said imaging of the secondary beamand outputting a signal to form a one-dimensional or two-dimensionalimage of a surface of the substrate; and generating an electromagneticwave and causing the electromagnetic wave to irradiate a location on thesurface of the substrate at which the secondary beam is generated;wherein a wavelength of the electromagnetic wave is defined on the basisof a potential barrier in a region of the surface layer in which theplurality of different materials contact each other.